NUTRITION. 57 



poured in unceasing flow from the centre of our 

 system. Can any thing more completely dis- 

 play a system of the loftiest design, and most 

 perfect order, than these phenomena?"* 



44. It has been shown that the watery 

 juices, pumped up as it were, by the roots, have 

 been drawn to the leafy parts ; a large part of 

 the water is there evaporated, green matter is 

 formed, and the decomposition of carbonic acid, 

 ammonia, and water, fixes carbon, nitrogen, and 

 hydrogen in the residuum. From these changes, 

 to which the term assimilation has been given, 

 results the formation of a new and descending 

 juice whose existence is perhaps less palpable 

 than that of the ascending sap, but concerning 

 which there can be no doubt. If a circular in- 

 cision be made in the bark of an exogenous tree ? 

 a tumour will in a short time appear above the 

 wound ; this tumour increases, and if the cut be 

 very narrow, it soon reaches the lower lip of 

 the wound, the communication is restored, and 

 the tree lives on as usual, but if the wound be 

 too wide to admit of this junction, the tumour 

 continues to increase till the branch (or the 

 tree, if the main trunk have been operated on) 



* Researches on Light, p. 200. 



